FIG. 1 illustrates a prior art refrigerated trailer 20. The trailer 20 includes a body formed from a pair of rectangular sidewalls 22, a front wall 26 and, rear doors (not shown) which extend upwardly from a floor structure 28, and a roof structure 30. The front wall 26 has a cooling unit 27 provided thereon in a conventional manner. The rear portion of the floor structure 28 is supported by a conventional rear undercarriage assembly 29. The front portion of the floor structure 28 has a conventional landing gear 34 secured thereunder. The roof structure 30 and an upper portion of each sidewall 22 is secured to a respective top rail 35 in a conventional manner. The floor structure 28 and a lower portion of each sidewall 22 is secured to a respective bottom rail 49 in a conventional manner. The top and bottom rails 35, 49 are made of a suitable material such as aluminum. The trailer 20 can be connected to a tractor by conventional means, such as a fifth wheel assembly.
As shown in FIG. 2, the sidewalls 22 are formed in a conventional manner. While one embodiment of a prior art sidewalls 22 is shown, this is not limiting and there are other embodiments known in the prior art. As shown, each sidewall 22 has an inner thin skin 43, an outer thin skin 47, and at least one “Z” shaped post 46 therebetween. The inner and outer skins 43, 47 are preferably made of fiberglass and aluminum, respectively, but can be any combination. Each post 46 is integrally formed of suitable structural material, such as aluminum or fiberglass polyester pultrusion. The posts 46 are generally mounted between the inner and outer skins 43, 47 of the sidewalls 22 and are spaced apart from each other along the length of each sidewall 22. When assembled, the inner skin 43 is spaced from the post 46 such that a cavity is formed. A generally L-shaped seal 69 is provided at the bottom of the cavity to separate the sidewall 22 from the floor structure 28. A foam is poured or injected between the inner skin 43 and the outer skin 47 to provide a foam core 48, to complete construction of the side wall 22. With the foam core 48 in place, the inner skin 43 is bonded to the post 46.
Each bottom rail 49 extends the length of the respective sidewall 22 and is connected to the sidewall 22 in a known manner. Each bottom rail 49 has a vertical portion 60 and a horizontal portion 62 at approximately a midpoint thereof which separates the vertical portion 60 into an upper vertical portion and a lower vertical portion. A generally Z-shaped member 51 is seated against the underside of the horizontal portion 62. The member 51 is formed of extruded aluminum and extends along the length of each bottom rail 49. Each member 51 has a horizontal upper leg 64 which is secured to the underside of the horizontal portion 62, a vertical intermediate leg 66 which extends downwardly from the upper leg 64, and a horizontal lower leg 68 which extends inwardly toward the interior of the trailer 20 from the lower end of the vertical intermediate leg 66.
The floor structure 28 includes floor material 44, which may be formed of, for example, aluminum or wood planks, raised up off structural floor supporting beams or crossmembers 45 by insertion of structural thermal risers 50 between the floor material 44 and the crossmembers 45. The risers 50 generally align with the crossmembers 45. Each end of the crossmembers 45 has an end clip 52 that is connected to the lower vertical portion of the respective bottom rail 49 by suitable means, such as rivets or bolts. A plurality of the cross-members 45 are provided at spaced apart locations along the bottom rail 49. Each cross-member 45 is integrally formed from a conventionally formed I-beam. A barrier sheet or subpan 41 is sandwiched between the crossmembers 45 and the floor risers 50. The space between the floor material 44 and the subpan 41 creates a cavity in which the core 25, formed from an insulating material, such as urethane foam, can be poured or injected to fill the cavity.
The subpan 41 is formed of a flat sheet of material which is seated onto the upper surface of the horizontal lower leg 68. When the core 25 is foamed into place, the pressure from the foam seals the subpan 41 against the horizontal lower leg 68. Therefore, no fastening means are required. Fastening means can, however, be provided.
Various sheet materials have been employed as a refrigerated trailer subpans through the years. Early designs were steel that was heavy and rusted badly. In the 1960's aluminum was substituted for steel but galvanic corrosion at the steel structural floor support was not much of an improvement. Later, a polyester fiberglass reinforced plastic sheet (FRP) became the most popular material as it could be made light weight, strong and corrosion free.
Around year 2000, a new process was created for forming a woven FRP 70 (see FIGS. 3A and 3B). In this new process, glass fibers were impregnated with a thermoplastic resin. The resin and glass fibers were simultaneously produced and then co-mingled into a roving 71. Multiple rovings 71 were then woven into a cloth and as a result, the glass fibers extended in both the X and Y directions. Heat and pressure were applied to the cloth to melt the thermoplastic resin fibers, fusing the glass fibers together. Cooling the hot sheet under pressure produced a woven FRP sheet 70 that was very strong and light weight. Because the glass fibers are interlocked as a result of the weaving, the bundles of fibers (strand) cannot pull out of the consolidated sheet 70. The thermoplastic FRP sheet 70 is tough and proved to be superior to the polyester sheet which was brittle. Therefore, the more efficient woven thermoplastic FRP sheet 70 became the standard in many applications. This thermoplastic FRP sheet 70 still, however, had a basic problem. Pin holes 33 would develop in the consolidated sheet 70 at the intersection of the rovings in the weave, see FIG. 3A. A thin FRP sheet (not shown) was added to prevent the pinhole problem. This made the product less cost efficient but the woven resin sheet was still superior to the polyester sheet. Alternatively, extra resin and fibers were added to fill the pin holes 33. This form of reinforcement is very strong and energy absorbing, but it is also expensive. In the woven thermoplastic FRP sheet 70 shown in FIGS. 3A and 3B, the fibers weave back and forth in the woven cloth. When the woven FRP sheet 70 is stressed, the fibers tend to straighten before stressing takes place. This form of reinforcement tends to be more flexible, but increases its energy absorption impact properties.
Another prior art configuration using FRP is shown in FIGS. 4A and 4B. This configuration uses random chopped fibers 34 to form the sheet 80. The fibers 34 are completely randomly place, similar to a compressed stack of hay.
Due to the ease of processing the sheet 80 and due to the fact that this is one of the most cost effective methods of reinforcing the resin available, reinforcements of this type have been very popular. Reinforcements of this type, however, tend to be less efficient at reinforcing the resin. The woven thermoplastic FRP sheet 70 shown in FIGS. 3A and 3B presents several advantages over the sheet 80 of FIGS. 4A and 4B. As a result of weaving the reinforcing fibers, the tear resistance and strength properties are improved over the sheet 80. Bundles of parallel fibers that have been locked in place by the weave work together, as opposed to the random chopped fibers which are oriented in all directions. However, the cost of weaving is significant and woven cloth has to be sized and inventoried for the application or considerable waste will occur.
To eliminate weaving costs, various methods of non-woven unidirectional fiber reinforcements have been used. For example, stitching or sewing parallel fibers eliminates weaving, The non-woven parallel fibers in place so they can be handled like the woven fiber cloth. Multiple layers of the stitched fibers are layered and then stitched together to produce a cloth with fiber reinforcement in various directions. The stitched cloth fibers stay in place while they are saturated with a liquid resin.
The present invention provides a reinforcement sheet which overcomes the problems presented in the prior art and which provides additional advantages over the prior art, such advantages will become clear upon a reading of the attached specification in combination with a study of the drawings.